Institute of Virology, Philipps University of Marburg, Marburg, Germanya; Faculty of Chemistry, University of Bielefeld, Bielefeld, Germany.
J Virol. 2012 Apr;86(7):3736-45. doi: 10.1128/JVI.06628-11. Epub 2012 Jan 25.
Proteolytic activation of the fusion protein of the highly pathogenic Nipah virus (NiV F) is a prerequisite for the production of infectious particles and for virus spread via cell-to-cell fusion. Unlike other paramyxoviral fusion proteins, functional NiV F activation requires endocytosis and pH-dependent cleavage at a monobasic cleavage site by endosomal proteases. Using prototype Vero cells, cathepsin L was previously identified to be a cleavage enzyme. Compared to Vero cells, MDCK cells showed substantially higher F cleavage rates in both NiV-infected and NiV F-transfected cells. Surprisingly, this could not be explained either by an increased F endocytosis rate or by elevated cathepsin L activities. On the contrary, MDCK cells did not display any detectable cathepsin L activity. Though we could confirm cathepsin L to be responsible for F activation in Vero cells, inhibitor studies revealed that in MDCK cells, cathepsin B was required for F-protein cleavage and productive replication of pathogenic NiV. Supporting the idea of an efficient F cleavage in early and recycling endosomes of MDCK cells, endocytosed F proteins and cathepsin B colocalized markedly with the endosomal marker proteins early endosomal antigen 1 (EEA-1), Rab4, and Rab11, while NiV F trafficking through late endosomal compartments was not needed for F activation. In summary, this study shows for the first time that endosomal cathepsin B can play a functional role in the activation of highly pathogenic NiV.
高度致病性尼帕病毒（NiV F）融合蛋白的蛋白水解激活是产生感染性颗粒和通过细胞间融合进行病毒传播的前提。与其他副粘病毒融合蛋白不同，功能性 NiV F 激活需要内吞作用和 pH 依赖性在内体蛋白酶的单碱性裂解位点裂解。使用原型 Vero 细胞，先前已鉴定组织蛋白酶 L 是一种裂解酶。与 Vero 细胞相比，MDCK 细胞在 NiV 感染和 NiV F 转染细胞中均显示出明显更高的 F 裂解率。令人惊讶的是，这既不能通过增加 F 内吞作用率来解释，也不能通过提高组织蛋白酶 L 活性来解释。相反，MDCK 细胞没有显示出任何可检测到的组织蛋白酶 L 活性。虽然我们可以确认组织蛋白酶 L 在 Vero 细胞中负责 F 激活，但抑制剂研究表明，在 MDCK 细胞中，组织蛋白酶 B 是 F 蛋白裂解和致病性 NiV 复制所必需的。支持 MDCK 细胞早期和再循环内体中有效 F 裂解的想法，内吞的 F 蛋白和组织蛋白酶 B 与内体标记蛋白早期内体抗原 1（EEA-1）、Rab4 和 Rab11 明显共定位，而 NiV F 通过晚期内体区室的运输对于 F 激活不是必需的。总之，这项研究首次表明，内体组织蛋白酶 B 可以在高度致病性 NiV 的激活中发挥功能作用。
